But his lawyers are arguing that he had acted in self-defence - after a theft gone wrong.

However, Associate Professor Gilbert Lau (below), a senior consultant forensic pathologist who had performed the autopsies of the father and son, said if that had been the case, the one going through an autopsy would have been the accused, Iskandar Rahmat, instead.

Prof Lau was testifying yesterday at Iskandar's murder trial, where he is accused of killing Mr Tan Boon Sin, 67, and his son, Mr Tan Chee Heong, 42, in 2013.

He told the court that the elder Mr Tan had 12 stab wounds on his neck and chest, including a 13cm-deep wound on his chest, and at least nine slash wounds on his neck, face, head and chest.

He also had a number of defensive injuries on his hands. The most fatal injury was a deep cut across his neck which had severed a main artery.

In a spirited exchange with defence lawyer Shashi Nathan, Prof Lau rejected the defence's suggestion that Mr Tan Boon Sin had attacked an unarmed Iskandar, who then reacted in self-defence.

And if the wounds on Mr Tan Boon Sin were a result of Iskandar acting in self-defence, why not simply stab him once, twice, or even thrice but why 12 times, Prof Lau asked.

"To me, that would seem quite an excessive form of self-defence. Also, if I'm not mistaken, (Iskandar) is a much younger man than Mr Tan Boon Sin. I really find it very difficult to believe (that he acted in self-defence)," Prof Lau said.

He had also earlier raised the possibility that a second knife could have been used in the attacks after being shown Iskandar's drawing of the alleged murder weapon, which showed a knife with a serrated edge.

While most of the stab wounds on the victims had regular and clean-cut margins, there were some wounds with irregular borders.

"I did consider that (the) assailant used more than one," he added.

But when asked about the sequence of the stabbing, Prof Lau bristled, saying it is something pathologists are cautioned against doing because stabbing is a dynamic situation where both assailant and victim are moving.

"It is very difficult to determine the precise sequence (of stabs). It might be possible in CSI (a popular TV show about forensic investigation), but not in real life," he said.

As for Mr Tan Chee Heong, he had seven stab wounds on his face and neck, with the death blow being one on the right side of his neck that had severed a main artery. He also had six cuts of various depths on his neck and face, including one so deep it exposed the bone of his right temple, which had been fractured.

His body being dragged on the road had also led to several abrasive injuries, though they were unlikely to have worsened his condition.

(Defence lawyer) Mr Shashi's proposition is that it was Mr Tan Boon Sin who first thrust a knife at (Iskandar), who at the time was allegedly unarmed. If that is in fact the case, then I surmise... I would be conducting the autopsy on his client (Iskandar) instead of Mr Tan Boon Sin.

A caretaker and a domestic worker who worked in buildings surrounding 14J, Hillside Drive, saw similar versions of what happened on the afternoon of July 10, 2013.

Mr Anthony Fabian, 56, who worked as a caretaker of a disused school building at 11, Hillside Drive, was sweeping the grounds when he heard a commotion.

Walking to the main gate to get a better look, he heard a thud and saw Mr Tan Chee Heong lying on the ground outside 14J, Hillside Drive.

Shortly after, he heard the engine of a silver Toyota Camry start and saw the car reverse over Mr Tan's body.

"I saw it go over (the man). He was in between the tyres and the body was under the car," Mr Fabian said.

He added that he saw the body get dragged along Hillside Drive towards Upper Serangoon Road.

"I could see the legs of the man protruding out from below the car and I ran after it to try to stop the driver."

Along the way, he passed a mosque, where he alerted a man standing outside about what was going on. The man then chased the car on his motorcycle.

Mr Fabian also called the police to report the incident and waited till the first responder, a traffic police officer, arrived.

Former Indonesian domestic worker Salamah, 28, also testified that she had seen Mr Tan stumble out of the house.

She was washing crockery near the back of her employer's home at about 3.30pm when she heard shouting coming from 14J, Hillside Drive.

Going to the fence to take a closer look, Madam Salamah said she saw Mr Tan stumble out of the house clutching his neck, his body covered in blood.

He collapsed face down on the road in front of the house and more blood gushed out of him.

RECOGNISED HIM

Speaking through a Bahasa Indonesia interpreter, Madam Salamah said she recognised Mr Tan because he visited his parents frequently, parking his red car on the road between Madam Salamah's employer's house and 14J, Hillside Drive.

Madam Salamah said she saw the accused, Iskandar Rahmat, walk around the back of the car. After he saw Mr Tan lying on the ground, he walked back towards the driver's door.

She then heard the car engine start and could hear the sound of something being dragged, but could not see what it was.

After the car headed towards the main road, Madam Salamah noticed the body was no longer there and all that remained was a large pool of blood.

When pressed repeatedly by Iskandar's lawyer on whether she had actually seen him walk around the back of the car despite her slight stature and the height of the fence, Madam Salamah said yes.

Older victim had serious knee problems

BAD KNEE: Dr Kevin Lee diagnosed Mr Tan Boon Sin’s osteoarthritis.

Mr Tan Boon Sin was due for knee replacement surgery and his condition was so bad that he was bow-legged on his left leg, said an orthopaedic surgeon who treated him.

Dr Kevin Lee, who is in private practice, said he first saw Mr Tan in October 2011.

He diagnosed Mr Tan with osteoarthritis in his left knee, which meant that the cartilage in his knee had worn out due to degeneration.

Mr Tan had problems walking, standing up after sitting and had trouble climbing up and down stairs.

His left knee was in such a bad state that a knee replacement was the only option - it was only a question of whether to do a full or partial replacement - and an MRI had been scheduled for August 2013 to confirm this before the operation.

But if someone were to push Mr Tan while he was standing up, he would fall quite easily because he put most of his weight on his right leg, Dr Lee said in response to a question from the judge.

Also taking the stand was Dr Teo Eng Swee, who had examined Iskandar Rahmat's hand injuries.

The senior consultant forensic pathologist at the Health Sciences Authority noted that Iskandar had been cut by a sharp object and had two wounds on the web of his right hand, between the thumb and index finger.

Two of the wounds measured 2.5cm and 3cm.

Asked by Mr Nathan if he examined Iskandar's left hand, where a later examination had revealed bite marks, Dr Teo said he did not as he had been told to only examine the right.

ABOUT THE CASE

On July 10, 2013, the body of Mr Tan Chee Heong, 42, was found with stab wounds at a taxi stand outside Kovan MRT Station (below), where it had been dislodged after being dragged nearly 1km by a car owned by his father.

The blood trail led back to 14J, Hillside Drive, where the body of his father, Mr Tan Boon Sin, 67, was found with multiple stab wounds in his home.

Iskandar Rahmat, 36, then a police officer with the Bedok Police Division, is now on trial for the double murder.

Iskandar, who was facing disciplinary proceedings because of a $50,000 debt to OCBC Bank, fled to Malaysia that night. He was arrested in a popular Johor Baru eatery two days later.

The prosecution says that Iskandar had hatched an elaborate plan to rob and kill Mr Tan Boon Sin to alleviate his money problems.

His defence team, however, maintains that the incident was a theft gone wrong with tragic consequences.